1. Field of the Invention
The present invention relates to point-of-use vaporization systems for use in Chemical Vapor Deposition (CVD). More particularly, the present invention relates to systems which deliver a precursor to a vaporization point.
2. The Background Art
Point-of use-vaporization systems are known in which a liquid precursor is delivered to a vaporization point in the vaporization systems in order to vaporize the liquid precursor for use in Chemical Vapor Deposition (CVD). In CVD devices, the components of the film must arrive at a substrate where they undergo a chemical reaction. In such point-of-use vaporization systems, the liquid precursors pass to a porous frit comprising a metal sponge, such as stainless steel, or a series of discs, or some other vaporization surface, where the precursors are vaporized due to heat in the system and the frit. Once vaporized, the corresponding gases pass from the frit into a shower head and onto a substrate, such as a silicon wafer. The shower head introduces other materials to the gases, such as an oxidizer or Nitrogen, which react with the precursors to cause the coating of a film onto the wafer. Inert materials may also be added in the shower head to tailor the resulting film.
Suitable precursors comprise organic metallics, such as tantalum pentaethe oxide, barium(thd).sub.2.polyamine, strontium(thd).sub.2 Polyamine, or titanium(O-iPr).sub.2 (thd).sub.2 which may be mixed with a suitable solvent, such as, for example, butyl acetate. The vaporized precursor and solvent then pass to a wafer where the precursor forms a film on the wafer.
However, it has been found that the flow of precursors to the vaporization point can not be readily started, stopped, and changed in such systems. This is due to particle formation of the precursor, since the precursor can dry out and form undesired particles as the flow of the precursor is stopped. These particles may clog the frit. Also, there has been difficulty due to clogging of the precursor line as a result of extreme particle formation in the precursor. Additionally, there can be "first injection" effects due to the precursor coming in contact with dry point-of-use vaporization hardware, which may also cause the formation of particles on the frit, and nonstable vaporization conditions, which can be detrimental to film properties and deposition stability.
Prior vaporization systems have a passageway between the frit and shower head to deliver gases from the frit to the shower head. Such vaporization systems also have a first valve in the passageway to control the flow of gases between the frit and shower head, and a second valve for controlling the passage of gases between the passageway and an exhaust. However, such valves and associated hardware have significantly increased the cost and bulk of such systems.
U.S. Pat. No. 5,362,328 relates to the direct flushing of a precursor line with a solvent.